1. Field of the Invention
This invention relates to novel peracid esters usable as a radical polymerization initiator and a method of producing the same as well as hydroperoxides as a starting material for the peracid ester, and polymerization of vinyl monomer, curing of unsaturated polyester and crosslinking of polymer through the peracid ester.
2. Related Art Statement
In general, it is known to use t-alkyl peracid esters as a polymerization initiator, a curing agent or a crosslinking agent as described in, for example, Japanese Patent Application Publication No. 51-38752 and No. 62-30064, Japanese Patent laid open No. 52-76353 and the like.
In polymer industry, however, it is desired to increase the production of polymer resins without requiring additional construction of expensive production equipments from a viewpoint of economical reasons. Further, it is demanded to develop a more active polymerization initiator for shortening the reaction time and increasing the production volume.
As a polymerization technique, it is known that the polymerization rate can be increased by using the more active polymerization initiator. The production improvement through such a technique is particularly useful in the polymerization of vinyl chloride. Because, in the polymerization of vinyl chloride, the polymerization degree is determined by the polymerization temperature but is not dependent upon the polymerization rate. Therefore, even when the polymerization rate is increased by using the highly active polymerization initiator, if the polymerization temperature is constant, the polymerization degree is unchangeable. That is, the polymerization rate can be enhanced without changing the physical properties of the polymer.
Further, the more active polymerization initiator is desirable to be used for objects other than the above production improvement. That is, such an object is concerned with the production of polyvinyl chlorides having a high polymerization degree.
In general, polyvinyl chlorides having a polymerization degree of not less than 1500 are called as a high polymerization degree product and are known to be particularly excellent in the properties such as mechanical strength, heat stability, dimensional stability, cold resistance and the like.
Furthermore, when flexible polyvinyl chlorides are produced by adding a plasticizer to the polyvinyl chloride, rubbery elasticity can be enhanced as the polymerization degree becomes high.
As shown in the following Table 1, the polymerization degree of the polyvinyl chloride is determined by the polymerization temperature, so that in order to obtain a polyvinyl chloride having a high polymerization degree, vinyl chloride should be polymerized at a relatively low temperature of not higher than 50.degree. C. From this reason, it is desired to develop a polymerization initiator having a sufficient activity even at a low temperature.
TABLE 1 ______________________________________ Polymerization temperature Polymerization (.degree.C.) degree ______________________________________ 60 800 57 1000 52 1300 50 1500 45 2000 40 2500 35 3000 ______________________________________
It has hitherto been known to use diisobutyryl peroxide (hereinafter abbreviated as IBPO), acetylcyclohexylsulfonyl peroxide (hereinafter abbreviated as ACSP, Japanese Patent Application Publication No. 40-16795) or the like as a polymerization initiator having an activity even at the low temperature when polymerizing vinyl chloride monomer.
Furthermore, peracid esters such as cumylperoxy neodecanoate (hereinafter abbreviated as CND, Japanese Patent laid open No. 58-120611), t-octylperoxy neodecanoate (hereinafter abbreviated as OND, Japanese Patent laid open No. 58-120613) and the like have been known as a polymerization initiator.
However, there are some problems in the polymerization methods using IBPO, ACSP, CND or OND as a polymerization initiator. That is, IBPO is very unstable against water and is decomposed by contacting with water, so that the polymerization activity is not held and hence the yield of the polymer is low. On the other hand, ACSP has a problem in view of the hygiene of decomposition product and is poor in the heat stability because the resulting polymer is colored. Furthermore, CND produces a peculiar odor in the polymer because of the decomposition product. Moreover, OND hardly affects the properties of the resulting polymer, but is poor in the polymerization activity as compared with ACSP, CND and the like, so that it is small in the effect as a polymerization initiator having an activity at low temperature.
In the field of peroxides, it is well-known that the half-valued period of a certain peroxide (measure on the activity of the peroxide) is remarkably changed by applying various structure variations to the peroxide. For example, in case of an alkyl peracid ester, the activity can be changed by the structure variation of carboxylic group and alkylperoxy group.
The alkyl peracid ester obtained by the conventional technique and having an activity at a lowest temperature is a compound in which the alkylperoxy group is t-octylperoxy group. This compound has an activity at a low temperature as compared with the other peracid ester containing, for example, t-butylperoxy group, t-amylperoxy group, t-hexylperoxy group or the like when the carboxylic group is same.
A temperature requiring that a half-valued period of 1 mol/ l of t-butylperoxy neodecanoate, t-amylperoxy neodecanoate or t-hexylperoxy neodecanoate in benzene is 10 hours (hereinafter referred to as 10 hour halflife temperature) is 45.degree.-47.degree. C., while the 10 hour halflife temperature of OND is as low as 41.degree. C. As previously mentioned, however, it is further demanded to develop a polymerization initiator having an activity at a lower temperature in order to conduct low temperature polymerization for the shortening of polymerization time and the increase of production volume.